We have found that vaginal stimulation can facilitate lordosis in rats. Estrogen and progesterone increase the lordosis response intensity but the response occurs even in the absence of these hormones. The vaginal stimulation also induces behavioral immobility, which is so intense that when we pinch a foot, it is not withdrawn. We tested whether this effect was due to a blockage of noxious afferents by recording neuronal activity in the sensory thalamus. In neurons that were activated by pinch and touch, vaginal stimulation blocked the response to pinch but did not affect the response to touch. Vocalization in response to tail shock was also blocked by vaginal stimulation. Using a pain test which measures the latency to withdraw a leg during incremental foot compression, vaginal stimulation was more effective than morphine (2.0 mg/kg) in delaying the response. In pharmacological studies the pain blocking effect of vaginal stimulation seem to depend on the integrity of noradrenergic mechanisms. This is an example of a visceral stimulus (probing the vaginal cervix) influencing the somatic reflexes; it facilitates lordosis (an extensor reflex) and simultaneously blocks withdrawal (flexor) reflexes. Studies are in progress to elucidate whether these effects can be explained by convergence of afferent visceral (vaginal cervix) and somatic (flank-perineum input) onto the same spinal neurons. Their activity could summate in facilitating lordosis and somatic and/or visceral afferent activity could close a pain "gate". In addition to examining neural-hormonal interactions, these studies may elucidate the neural bases of visceral-somatic interactions, referred pain and acupuncture.